In article <1990Mar1.143905.14553@esegue.segue.boston.ma.us> hackeron@ATHENA.MIT.EDU writes:>Does anyone know of a compiler/language that allows you to specify changes>to how the language is parsed (in part at least) from withing the program.

Edinburgh-derived Prologs have a precedence grammar that can be
changed at runtime (though not all implementations let you change
everything); the interesting part of it is that you can change
operators between prefix, infix and postfix, and the system will, if
you wish, respect the new conventions on output also. This makes
reading and writing (certains kinds of) unusually-formatted stuff
almost painless. I once threw together a tiny natural-language-like
interface in a great hurry by this means. (Emphasis on TINY).